Cloning and expression of thermo-alkali-stable laccase of Bacillus licheniformis in Pichia pastoris and its characterization

A thermo-alkali-stable laccase gene from Bacillus licheniformis was cloned and expressed in Pichia pastoris. The recombinant laccase was secreted into the culture medium with a maximum activity of 227.9 U/L. The purified laccase is a monomeric glycoprotein, and its molecular weight was estimated to be 65 kDa on SDS–PAGE after deglycosylation. Optimal enzyme activity was observed at pH 6.2 and 70 °C with syringaldazine as substrate. The recombinant laccase was highly stable in the pH range 7–9 after 10 days at 30 °C. The enzyme displayed remarkable thermostability at 50–70 °C, with a half-life of inactivation at 70 °C of 6.9 h. It also exhibited high tolerance to NaCl and organic solvents like the native spore laccase. The purified laccase could rapidly decolorize reactive blue 19, reactive black 5 and indigo carmine in the presence of acetosyringone. More than 93% of the tested dyes were decolorized in 4 h at pH 9.0.